See Figures 1 and 2
All 1972 Fords manufactured for sale in California equipped with a 5.8L Cleveland (C) or 6.6L V8, and all 1972 Fords equipped with the 7.0L police interceptor engine, use the electronic spark control system.
Electronic Spark Control (ESC) is a system which blocks off carburetor vacuum to the distributor vacuum advance mechanism under certain temperature and speed conditions. The electronic spark control system consists of four components: a temperature sensor, a speed sensor, an amplifier, and a distributor modulator vacuum valve. The system serves to prevent ignition timing advance (by blocking off carburetor vacuum from the distributor vacuum advance mechanism) until the car reaches a speed of 35 mph (56 kmph) when the ambient temperature is over 65°F (18°C).
The temperature sensor, which is mounted on the front face of the left door pillar, monitors the outside air temperature and relays this information to the amplifier. The amplifier, which is located under the instrument panel, controls the distributor modulator vacuum valve. The modulator valve, which is attached to the ignition coil mounting bracket, is connected into the carburetor vacuum line to the distributor, and is normally open. If the temperature of the outside air is below 48°F (9°C), the contacts in the temperature sensor are open and no signal is sent to the amplifier. Since no signal is sent to the amplifier, the amplifier does not send a signal to the distributor modulator valve, and the vacuum passage from the carburetor to the distributor vacuum advance remains open. When the outside temperature rises to 65°F (18°C) or above, the contacts in the temperature sensor close, and a signal is sent to the amplifier. The amplifier relays the message to the distributor modulator, which closes to block the vacuum passage to the distributor, preventing ignition timing advance.
When the ambient temperature is 65°F (18°C) or above, ignition timing advance is prevented until the amplifier receives a signal from the speed sensor that the speed of the vehicle has reached 35 mph (56 kmph), and the distributor modulator vacuum valve can be opened to permit ignition timing advance.
The speed sensor is a miniature generator which is connected to the speedometer cable of the car. As the speedometer cable turns, the inside of the speed sensor turns with the speedometer cable. As the speed of the car increases, a rotating magnet in the speed sensor induces an electronic current in the stationary winding in the speed sensor. This current is sent to the amplifier. As the speed of the vehicle increases, the amount of current sent to the amplifier by the speed sensor increases proportionately. When the car reaches a speed of 35 mph (56 kmph), the amplifier signals the distributor modulator vacuum valve to open, allowing carburetor vacuum to be sent to the distributor vacuum advance chamber. This permits the ignition timing to advance.
It should be noted that this system operates only when the ambient temperature is 65°F (18°C) or above, and then only when the speed of the car is below 35 mph (56 kmph).
- Raise the car until the rear wheels are clear of the ground by at least 4 in. (102mm). Support the rear of the car with jackstands.
- Disconnect the vacuum hose from the distributor vacuum advance chamber. This is the outer hose.
- Connect the hose to a vacuum gauge.
- Pour hot water on the temperature sensing switch to make sure that it is above 65°F (18°C).
- Start the engine and apply the foot brake. Depress the clutch and shift the transmission into high gear, if equipped with a manual transmission. If equipped with an automatic transmission, shift into DRIVE and push on the gas pedal.
- Have an assistant observe the vacuum gauge while you raise the speed of the engine until the speedometer reads 35 mph (56 kmph), at which time the vacuum gauge should show a reading.
- If the vacuum gauge shows a reading below 35 mph (56 kmph), a component in the electronic spark control system is defective. If the vacuum gauge does not show a reading, even above 35 mph (56 kmph), there is either a defective component in the electronic spark control system, or there is a broken or clogged vacuum passage between the carburetor and the distributor.
REMOVAL & INSTALLATION
- Open the right door and remove the two screws which attach the temperature sensor to the right door pillar.
- Disconnect the lead wires from the temperature sensor.
- Remove the sensor.
- Connect the lead wires to the new sensor.
- Position the sensor on the door pillar and install the attaching screws.
- Disconnect the lead wires from the sensor.
- Disconnect the speed sensor from the speedometer cable.
- Position the O-rings on both ends of the new speed sensor.
- Connect both ends of the speedometer cable to the speed sensor.
- Connect the lead wires to the speed sensor.
- Locate the amplifier under the instrument panel, near the glove compartment.
- Disconnect the wiring harness from the amplifier.
- Remove the two amplifier attaching screws and remove the amplifier.
- Position a new amplifier under the instrument panel and connect the wiring harness to it.
- Install the two amplifier attaching screws
Distributor Vacuum Modulator Valve
- Tag the hoses that attach to the modulator and disconnect them from the amplifier.
- Disconnect the lead wires from the modulator.
- Remove the No. 2 left front valve cover bolt (6 cylinder) or the inboard left front valve cover bolt and remove the modulator.
- Position the new modulator on the valve cover and install the attaching bolt.
- Connect the wires and hoses to the modulator.